Microfluidics generally refers to microfabricated devices, which are used for pumping, sampling, mixing, analyzing and dosing liquids. Prominent features thereof originate from the peculiar behavior that liquids exhibit at the micrometer length scale. Flow of liquids in microfluidics is typically laminar. Volumes well below one nanoliter can be reached by fabricating structures with lateral dimensions in the micrometer range. Reactions that are limited at large scales (by diffusion of reactants) can therefore be accelerated.
Many microfluidic devices have user chip interfaces and closed flowpaths. Closed flowpaths facilitate the integration of functional elements (e.g. heaters, mixers, pumps, signal detector, valves, air vents, etc.) into one device while minimizing problems related to leaks and evaporation.
Most of the microfluidic chips are made in polymer or silicon (Si). Si microfluidic chips have a number of advantages for performing bioassays but these chips are expensive to fabricate and integrating reagents into Si chips is difficult. The price of Si microfluidic chips scales with their area and both the Si wafers and microfabrication techniques are expensive. One reason why it is difficult to integrate reagents in Si chips with a two-dimensional (2D) flow path is that all operations (loading sample, monitoring signal, integrating reagents, etc.) usually have to be performed on the side of the chip that exhibits the flow path. The depth of structures is limited by the need to keep a minimal residual thickness of the underlying silicon material (to maintain adequate mechanical properties). Thus, the reservoirs and capillary pumps have a limited thickness, which needs be compensated by a large area.